The biosynthesis, mechanistic enzymology and molecular genetics of terpenoid biosynthesis in bacteria and fungi will be investigated, with particular emphasis on the mechanistic and structural characterization of three broad classes of proteins uncovered by mining of genomic databases and functional gene expression that present novel structural, mechanistic, or biological features: 1) Investigations of terpene synthases will focus on defining the cyclization mechanisms and elucidating the role of each protein in catalyzing the formation of its individual cyclization products. A combination of bioinformatic tools as well as mutational approaches will be used to identify targets that represent new structural types or unusual biosynthetic reactions and mechanisms, or that correspond to cryptic synthases of currently unknown function that are implicated in biologically important processes such as fungal virulence. The mechanistic focus will be on discovering new cyclases and on unraveling the protein structural basis for catalysis and product specificity using a combination of site-directed mutagenesis and protein crystallography. 2) A variety of catalytically novel oxygenases will be investigated that play key roles in the metabolic conversion of terpene hydrocarbons and alcohols to biosynthetic end-products. 3) The regulation of microbial terpene biosynthesis will also be probed, focusing on two intriguing model systems, the regulation of the biosynthesis of the antibiotic pentalenolactone and the exploration of the cryptic role of a highly conserved nucleotide-binding protein associated with the biosynthetic genes for the widely occurring volatile organic metabolite 2-methylisoborneol. Tens of thousands of terpenoid natural products are present in both terrestrial and marine plants, in fungi and liverworts, and numerous bacteria. Many of these compounds are widely used in human medicine such as the antitumor agent taxol or the antimalarial artemisinin, or harmful to human and animal health, such as the widely occurring trichothecene mycotoxins. Many terpenoids are known plant or fungal hormones, plant protectants, or microbial virulence factors. The ubiquitous volatile bacterial organics geosmin and methylisoborneol, which are responsible for the characteristic odor of moist soil, are also the cause of periodic, widely occurring, and costly episodes of unpleasant taste and odor in public drinking water supplies and in aquaculture. Beyond the intrinsic biological importance of terpenoid metabolites, the study of microbial terpene biochemistry, structural biology, and molecular genetics provides a unique platform for the discovery of new biochemical reactions and mechanisms, for the understanding of the molecular logic of natural product biosynthetic pathways, for the elucidation of the still obscure factors regulating expression of these pathways, and for the coordinated application of biochemical, structural biological, bioinformatic, and molecular genetics tools to the understanding of microbial metabolism.